Poly(arylene ether)s are a class of plastics known for excellent water resistance, dimensional stability, and inherent flame retardancy, as well as high oxygen permeability and oxygen/nitrogen selectivity. Properties such as strength, stiffness, chemical resistance, and heat resistance can be tailored by blending poly(arylene ether)s with various other plastics in order to meet the requirements of a wide variety of consumer products, for example, plumbing fixtures, electrical boxes, automotive parts, and insulation for wire and cable.
Injection molding compositions including a poly(arylene ether), a rubber-modified polystyrene, and a flame retardant are commonly used to mold a variety of articles. These compositions are often explicitly characterized according to physical properties of molded test articles prepared from them, including objective metrics of stiffness (for example, flexural modulus), ductility (for example, notched Izod impact strength and tensile elongation at break), and heat resistance (for example, heat deflection temperature). Surface esthetics are often an uncommunicated critical-to-quality metric for plastic articles prepared by injection molding. One type of surface defect for injection-molded parts is a variation in color at the portions of the article corresponding to the injection molding gates of the injection molding machine. For example, a darkened ring can appear, as illustrated in FIG. 1. This is particularly a problem for molded parts with large, thin sections, such as, for example, plastic cases for the back-up batteries used in cell phone relay towers. The visual nonuniformities in the molded parts can lead to increased scrap rates and reduced productivity. And when the injection molded article is a case for a lead-acid battery, the presence of darkened rings can raise questions about whether the battery is leaking.
There is therefore a need for molding methods that reduce visual defects in the large, thin sections of articles molded from poly(arylene ether) compositions.